This afternoon, for the first time I can remember in 18 months of running this Zimbra server, the CPU utilisation (usr+sys) jumped up to 100%. Restarting Zimbra sees things calm down for a few minutes but it's soon back at 100%.
I upgraded to 4.5.10 a week ago, but haven't seen any problems over the last week. There were no administration changes made today, but it's possible that some users logged on today for the first time since the upgrade.
Here's the process that's using all the CPU:
The only thing I can see in the logs is SMPTD connections being made and dropped at a rate of one every few seconds, which isn't normal. All the connections come from the server itself.
zimbra 1908 1907 99 17:29 ? 04:19:19 /opt/zimbra/jdk1.6.0_02/bin/java -Xms607m -Xmx607m -client -XX:NewRatio=2 -Djava.awt.headless=true -Xss256k -Dcatalina.base=/opt/zimbra/apache-tomcat-5.5.15 -Dcatalina.home=/opt/zimbra/apache-tomcat-5.5.15 -Djava.io.tmpdir=/opt/zimbra/apache-tomcat-5.5.15/temp -Djava.library.path=/opt/zimbra/lib -Djava.endorsed.dirs=/opt/zimbra/apache-tomcat-5.5.15/common/endorsed -classpath /opt/zimbra/apache-tomcat-5.5.15/bin/bootstrap.jar:/opt/zimbra/apache-tomcat-5.5.15/bin/commons-logging-api.jar:/opt/zimbra/lib/jars/zimbra-launcher.jar com.zimbra.cs.launcher.TomcatLauncher
Jan 7 21:28:03 myserver postfix/smtpd: disconnect from myserver.myhost.co.uk[xx.xx.xx.xx]
Jan 7 21:28:03 myserver postfix/smtpd: connect from myserver.myhost.co.uk[xx.xx.xx.xx]
Jan 7 21:28:03 myserver postfix/smtpd: 4C95F431829F: client=myserver.myhost.co.uk[xx.xx.xx.xx]
Jan 7 21:28:03 myserver postfix/cleanup: 4C95F431829F: message-id=<KmqrBzhSh0SG.1Yy8vsKH>